That's unnecessary, using $device (which in your case is an XML::XPath::Node object returned from $nodeset->get_nodelist())as the context is fine.

I'm doing this because $device is a node from a node list not from a nodeset so I can't do this:$subdevice = $device->find('/subdevice');

Yes, you can :-). The synopsis in the XML::XPath::NodeSet documentation shows that usage pattern.

I don't know the structure of your XML (you've not provided a sample), but that is exactly how this sort of this is usually done.

If I go into the debugger and look at $plantdata->{nodeset} and $device both seem to contain a hell of a lot more than just the node I want. Is there a way to turn a $device node back into a nodeset so that I can dig deeper into it rather than going back to $xp and starting again?

Now, why would you use a debugger to look in the XML::XPath::Node object? ;)

Actually, every node object returned from the initial XPath context has a references back to the main XPath context's XML DOM. That's likely what you're seeing in the debugger.

XML::XPath::Node objects must have the full context, otherwise you couldn't perform XPath queries like

$node->find('/foo/../../../bar[2]');

because the context wouldn't be there to traverse!

The moral of the story is to use DOM methods to traverse the XML DOM, not a debugger.